An example would be the double slit experiment with single photons (or electrons) where an interference pattern is still present even though there is only one particle at a time to pass through the sytem. The observation that the particle interferes with itself is hard to internalize, but is well described by the copenhagen intepretation of the wave function.

ah the blessed double slit experiment.

lets pause and note that scientific theories describe observation of reality, not reality itself. for almost 1500 years our best theory for predicting the movement of the wandering stars was ptolemy's hideous spirograph assemblage. heliocentrism was posited again and again, but nobody could make it work until johannes kepler in 1605, and even kepler's model was imperfect.

i consider copenhagen analogous to ptolemaic geocentrism. it is extremely ugly, it cannot possibly describe reality, but may be the best theory we have, in the sense that while the predictions it makes are limited, they are essentially accurate to the extent we can measure their accuracy.

but its shortcomings are enormous, not least of which being how abhorrently inelegant it is. it irks me that rather than say "well, we don't know, but there is some probabilistic shit that seems to hold true that at least allows us to do this, this and this" we instead are told that "teh universe is probabilistic and consequently we can do this, this and this".

i'm also not a fan of wave-particle duality. how can an ace be one and eleven? only if we all agree that it can be and operate as if this is true. so when it is convenient an ace is 11, but then we hit and get a 6 and suddenly the ace becomes 1 because now 1 is convenient. we can either freely admit that we don't know whats going on yet but we have a functional conceptual model which fulfils our immediate needs, or we can pretend that we have the answer, that the universe suddenly becomes hideously ugly and that aces are in a superposition of 1 and 11.